For many thousands of years, men grunted their way through supremely difficult tasks of a physical nature. These included but were not limited to hunting things, gathering things, building things, and growing things. It was significant that those millennia featured an abundance of such tasks, for the spears, arrows, knives, rods, and other tools all resembled their penis. With a daily handling of these items, the men were reminded that they had their own spear in need of use. Despite the grueling nature of their livelihoods, each man was able to remember to come back to their home and procreate with their wife. The human race would live on because the men spent their day handling rods.
With the onset of the Industrial Revolution, however, men began doing other things that often had nothing to do with phallic tools. Some may have been putting wheels on cars (round), others may have been bagging grain (amorphous). With this professional diversion from long and straight objects, it was important to help men retain memory of the part of their anatomy that would be necessary for perpetuating our species.
This is why, even today, men wear an accessory that not only reminds them of the shape of their penis, but ensures the retention this information by pointing to precisely where on their body this organ is to be found. Otherwise, the men in their post-Industrial jobs would forget about it, we would stop procreating, and our species would die.
This is why we need neckties.